Where does Throw stores it's message numbers

For RaiseError,the message number should exist in sys.messages( even for custom messages). For Throw(Denali), it will be what?

e.g. if I do as

BEGIN TRY
    SELECT 1/0 
END TRY
BEGIN CATCH 
    THROW 50002, 'Some custom message.', 5
END CATCH

I will receive

Msg 50002, Level 16, State 5, Line 5 Some custom message.

and we know that the valid range for THROW is between 50000 to 2147483647. That means these custom message numbers will be stored/declared somewhere(in some table)[for RaiseError it is in sys.messages]. So which is it? Although the predefined messages are still from sys.messages

N.B.~ It is for my own understanding

Thanks